N,N&#39;-di(arylalkyl)-substituted naphthalene-based tetracarboxylic diimide compounds as n-type semiconductor materials for thin film transistors

ABSTRACT

A thin film transistor comprises a layer of organic semiconductor material comprising a tetracarboxylic diimide naphthalene-based compound having, attached to each of the imide nitrogen atoms, a substituted or unsubstituted arylalkyl moiety. Such transistors can further comprise spaced apart first and second contact means or electrodes in contact with said material. Further disclosed is a process for fabricating an organic thin-film transistor device, preferably by sublimation deposition onto a substrate, wherein the substrate temperature is no more than 100° C.

FIELD OF THE INVENTION

The present invention relates to the useN,N′-bis[arylalkyl]naphthalene-1,4,5,8-bis(dicarboximide) compounds assemiconductor materials in n-channel semiconductor films for thin filmtransistors. The invention relates to the use of these materials in thinfilm transistors for electronic devices and methods of making suchtransistors and devices.

BACKGROUND OF THE INVENTION

Thin film transistors (TFTs) are widely used as switching elements inelectronics, for example, in active-matrix liquid-crystal displays,smart cards, and a variety of other electronic devices and componentsthereof. The thin film transistor (TFT) is an example of a field effecttransistor (FET). The best-known example of an FET is the MOSFET(Metal-Oxide-Semiconductor-FET), today's conventional switching elementfor high-speed applications. Presently, most thin film devices are madeusing amorphous silicon as the semiconductor. Amorphous silicon is aless expensive alternative to crystalline silicon. This fact isespecially important for reducing the cost of transistors in large-areaapplications. Application of amorphous silicon is limited to relativelylow speed devices, however, since its maximum mobility (0.5-1.0 cm²/Vsec) is about a thousand times smaller than that of crystalline silicon.

Although amorphous silicon is less expensive than highly crystallinesilicon for use in TFTs, amorphous silicon still has its drawbacks. Thedeposition of amorphous silicon, during the manufacture of transistors,requires relatively costly processes, such as plasma enhanced chemicalvapor deposition and high temperatures (about 360° C.) to achieve theelectrical characteristics sufficient for display applications. Suchhigh processing temperatures disallow the use of substrates, fordeposition, made of certain plastics that might otherwise be desirablefor use in applications such as flexible displays.

In the past decade, organic materials have received attention as apotential alternative to inorganic materials such as amorphous siliconfor use in semiconductor channels of TFTs. Organic semiconductormaterials are simpler to process, especially those that are soluble inorganic solvents and, therefore, capable of being applied to large areasby far less expensive processes, such as spin coating, dip coating andmicrocontact printing. Furthermore organic materials may be deposited atlower temperatures, opening up a wider range of substrate materials,including plastics, for flexible electronic devices. Accordingly, thinfilm transistors made of organic materials can be viewed as a potentialkey technology for plastic circuitry in display drivers, portablecomputers, pagers, memory elements in transaction cards, andidentification tags, where ease of fabrication, mechanical flexibility,and/or moderate operating temperatures are important considerations.

Organic materials for use as potential semiconductor channels in TFTsare disclosed, for example, in U.S. Pat. No. 5,347,144 to Garnier etal., entitled “Thin-Layer Field-Effect Transistors with MIS StructureWhose Insulator and Semiconductors Are Made of Organic Materials.”

Considerable efforts have been made to discover new organicsemiconductor materials that can be used in TFTs to provide theswitching and/or logic elements in electronic components, many of whichrequire significant mobilities, well above 0.01 cm²/Vs, and currenton/off ratios (hereinafter referred to as “on/off ratios”) greater than1000. Organic TFTs having such properties are capable of use forelectronic applications such as pixel drivers for displays andidentification tags. Most of the compounds exhibiting these desirableproperties are “p-type” or “p-channel,” however, meaning that negativegate voltages, relative to the source voltage, are applied to inducepositive charges (holes) in the channel region of the device.

As an alternative to p-type organic semiconductor materials, N-typeorganic semiconductor materials can be used in TFTs as an alternative top-type organic semiconductor materials, where the terminology “n-type”or “n-channel” indicates that positive gate voltages, relative to thesource voltage, are applied to induce negative charges in the channelregion of the device.

Moreover, one important type of TFT circuit, known as a complementarycircuit, requires an n-type semiconductor material in addition to ap-type semiconductor material. See Dodabalapur et al. in “Complementarycircuits with organic transistors” Appl. Phys. Lett. 1996, 69, 4227. Inparticular, the fabrication of complementary circuits requires at leastone p-channel TFT and at least one n-channel TFT. Simple components suchas inverters have been realized using complementary circuitarchitecture. Advantages of complementary circuits, relative to ordinaryTFT circuits, include lower power dissipation, longer lifetime, andbetter tolerance of noise. In such complementary circuits, it is oftendesirable to have the mobility and the on/off ratio of an n-channeldevice similar in magnitude to the mobility and the on/off ratio of ap-channel device. Hybrid complementary circuits using an organic p-typesemiconductor and an inorganic n-type semiconductor are known, asdescribed in Dodabalapur et al. (Appl. Phys. Lett. 1996, 68, 2264.), butfor ease of fabrication, an organic n-channel semiconductor materialwould be desired in such circuits.

Only a limited number of organic materials have been developed for useas a semiconductor n-channel in TFTs. One such material,buckminsterfullerene C60, exhibits a mobility of 0.08 cm²/Vs but isconsidered unstable in air. See R. C. Haddon, A. S. Perel, R. C. Morris,T. T. M. Palstra, A. F. Hebard and R. M. Fleming, “C₆₀ Thin FilmTransistors” Appl. Phys. Let. 1995, 67, 121. Perfluorinated copperphthalocyanine has a mobility of 0.03 cm²/Vs, and is generally stable toair operation, but substrates must be heated to temperatures above 100°C. in order to maximize the mobility in this material. See “NewAir-Stable n-Channel Organic Thin Film Transistors” Z. Bao, A. J.Lovinger, and J. Brown J. Am. Chem, Soc. 1998, 120, 207. Other n-channelsemiconductors, including some based on a naphthalene framework, havealso been reported, but with lower mobilities. See Laquindanum et al.,“n-Channel Organic Transistor Materials Based on NaphthaleneFrameworks,” J. Am. Chem, Soc. 1996, 118, 11331. One suchnaphthalene-based n-channel semiconductor material,tetracyanonaphthoquino-dimethane (TCNNQD), is capable of operation inair, but the material has displayed a low on/off ratio and is alsodifficult to prepare and purify.

Aromatic tetracarboxylic diimides, based on a naphthalene aromaticframework, have also been demonstrated to provide, as an n-typesemiconductor, n-channel mobilities up to 0.16 cm²/Vs using top-contactconfigured devices where the source and drain electrodes are on top ofthe semiconductor. Comparable results could be obtained with bottomcontact devices, that is, where the source and drain electrodes areunderneath the semiconductor, but a thiol underlayer needed to beapplied between the electrodes, which had to be gold, and thesemiconductor. See Katz et al. “Naphthalenetetracarboxylic Diimide-Basedn-Channel Transistor Semiconductors: Structural Variation andThiol-Enhanced Gold Contacts” J. Am. Chem. Soc. 2000 122, 7787; “ASoluble and Air-stable Organic Semiconductor with High ElectronMobility” Nature 2000 404, 478; Katz et al., European Patent ApplicationEP1041653 or U.S. Pat. No. 6,387,727. In the absence of the thiolunderlayer, the mobility of the compounds of Katz et al. was found to beorders of magnitude lower in bottom-contact devices. U.S. Pat. No.6,387,727 B1 to Katz et al. discloses fused-ring tetracarboxylic diimidecompounds, one example of which is N,N′-bis(4-trifluoromethylbenzyl)naphthalene-1,4,58,-tetracarboxylic acid diimide. Such compoundsare pigments that are easier to reduce. The highest mobilities reportedin U.S. Pat. No. 6,387,727 B1 to Katz et al. was between 0.1 and 0.2cm²/Vs, for N,N′-dioctyl naphthalene-1,4,5,8-tetracarboxylic aciddiimide.

Relatively high mobilities have been measured in films of naphthalenetetracarboxylic diimides having linear alkyl side chains usingpulse-radiolysis time-resolved microwave conductivity measurements. SeeStruijk et al. “Liquid Crystalline Perylene Diimides: Architecture andCharge Carrier Mobilities” J. Am. Chem. Soc. Vol. 2000, 122, 11057.

US Patent Pub. No. 2002/0164835 A1 to Dimitrakopoulos et al. disclosesimproved n-channel semiconductor films made of perylene tetracarboxylicacid diimide compounds, as compared to naphthalene-based compounds, oneexample of which is N,N′-di(n-1H,1H-perfluorooctyl)perylene-3,4,9,10-tetracarboxylic acid diimide. Substituents attached tothe imide nitrogens in the diimide structure comprise alkyl chains,electron deficient alkyl groups, electron deficient benzyl groups, thechains preferably having a length of four to eighteen atoms. Devicesbased on materials having a perylene framework used as the organicsemiconductor have led to low mobilities, for example 10⁻⁵ cm²/Vs forperylene tetracarboxylic dianhydride (PTCDA) and 1.5×10⁻⁵ cm²/vs forNN′-diphenyl perylene tetracarboxylic acid diimide (PTCDI-Ph). SeeHorowitz et al. in “Evidence for n-Type Conduction in a PeryleneTetracarboxylic Diimide Derivative” Adv. Mater. 1996, 8, 242 andOstrick, et al. J. Appl. Phys. 1997, 81, 6804.

As discussed above, a variety of 1,4,5,8-naphthalenetetracarboxylic aciddiimides have been made and tested for n-type semiconducting properties.In general, these materials, as an n-type semiconductor, have providedn-channel mobilities up to 0.16 cm²/Vs using top-contact configureddevices. There is a need in the art for new and improved organicsemiconductor materials for transistor materials and improved technologyfor their manufacture and use. There is especially a need for n-typesemiconductor materials exhibiting significant mobilities and currenton/off ratios in organic thin film transistor devices.

SUMMARY OF THE INVENTION

The present invention relates to n-channel semiconductor films for usein organic thin film transistors, of N,N′-di(arylalkyl) naphthalenetetracarboxylic diimide compounds having, attached to each of the twoimide nitrogens, an arylalkyl group, wherein the aryl group, which maybe substituted or unsubstituted, is attached via a divalent hydrocarbonto each imide nitrogen. Such films are capable of exhibiting, in thefilm form, the highest reported field-effect electron mobility, up to5.0 cm²/Vs for known n-type compounds. Such semiconductor films are alsocapable of providing device on/off ratios in the range of at least 10⁵.

One embodiment of the present invention is directed to the use of suchn-channel semiconductor films in organic thin film transistors eachcomprising spaced apart first and second contact means connected to ann-channel semiconductor film. A third contact means can be spaced fromsaid first and second contact means and adapted for controlling, bymeans of a voltage applied to the third contact means, a current betweenthe first and second contact means through said film. The first, second,and third contact means can correspond to a drain, source, and gateelectrode in a field effect transistor.

Another aspect of the present invention is directed to a process forfabricating a thin film transistor, preferably by sublimation orsolution-phase deposition of the n-channel semiconductor film onto asubstrate, wherein the substrate temperature is at a temperature of nomore than 100° C. during the deposition.

More particularly, the present invention is directed to an articlecomprising, in a thin film transistor, a thin film of organicsemiconductor material that comprises an N,N′-di(arylalkyl)-substitutednaphthalene-based tetracarboxylic diimide compound having a substitutedor unsubstituted carbocyclic aromatic ring system attached to each imidenitrogen atom through a divalent hydrocarbon group, wherein any optionalsubstituents on the aryl rings comprises at least one electron donatingorganic group, i.e., if one or more substituents are present on one orboth of the two carbocyclic ring systems, such substituents comprise atleast one electron donating group.

In one embodiment of the present invention, N,N′-di(arylalkyl)naphthalene-based tetracarboxylic diimide compounds are represented bythe following structure:

wherein, X is a divalent —CH₂— or alkyl-substituted —CH₂— divalentgroup, n=1, 2 or 3, and R¹, R², R³, R⁴, R⁵ (on a first ring system,preferably a first phenyl ring) and R⁶, R⁷, R⁸, R⁹, and R¹⁰ (on a secondring system, preferably a second phenyl ring) are each independently Hor an electron donating organic group, wherein optionally any twoadjacent R groups on a ring system can combine to form a fused aromatic,preferably a fused phenyl ring. Preferably, R¹, R², R³, R⁴, R⁵, R⁶, R⁷,R⁸, R⁹, and R¹⁰ on the aryl ring systems comprises at least one electrondonating group, most preferably a C1-C8 alkyl substituent. Preferredorganic groups include, for example, CH₃, linear or branched C2-C4alkyl, C1-C8 alkylene (a monovalent unsaturated aliphatic hydrocarbon),or C1-C8 alkoxy.

It is preferred that at least two of R¹, R², R³, R⁴ and R⁵ are H and atleast two of R⁶, R⁷, R⁸, R⁹, and R¹⁰ are H. More preferred structuresare those in which at least three of R¹, R², R³, R⁴ and R⁵ are H and atleast three of R⁶, R⁷, R⁸, R⁹, and R¹⁰ are H. Still more preferredstructures are those in which either all of R¹, R³, R⁴, R⁵, R⁶, R⁸, R⁹,and R¹⁰ are H, and both R² and R⁷ is an electron donating group,preferably an alkyl group such as CH₃; or all of R², R³, R⁴, R⁵, R⁷, R⁸,R⁹, and R¹⁰ are H, and both R¹ and R⁶ are an electron donating group,preferably an alkyl group such as CH₃. Preferably, at least one of saidaryl ring systems is substituted with a C1 to C4 containing alkyl group.

In the above Structure I, a first and second dicarboxylic imide moietyis attached on opposite sides of the naphthalene nucleus, at the 1,4 and5,8 positions of the naphthalene nucleus. The naphthalene nucleus can beoptionally substituted with up to four independently selected Y groups,wherein m is any integer from 0 to 4.

Advantageously, an n-channel semiconductor film used in a transistordevice according to the present invention does not necessarily require,for obtaining high mobilities, prior treatment of the first and secondcontact means connected to the film. Furthermore, the compounds used inthe present invention possess significant volatility so that vapor phasedeposition, where desired, is available to apply the n-channelsemiconductor films to a substrate in an organic thin film transistor.

As used herein, “a” or “an” or “the” are used interchangeably with “atleast one,” to mean “one or more” of the element being modified.

As used herein, the terms “over,” “above,” and “under” and the like,with respect to layers in the organic thin film transistor, refer to theorder of the layers, wherein the organic thin film layer is above thegate electrode, but do not necessarily indicate that the layers areimmediately adjacent or that there are no intermediate layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become more apparent when taken in conjunction with thefollowing description and drawings wherein identical reference numeralshave been used, where possible, to designate identical or analogousfeatures that are common to the figures, and wherein:

FIG. 1 illustrates a cross-sectional view of a typical organic thin filmtransistor having a bottom contact configuration; and

FIG. 2 illustrates a cross-sectional view of a typical organic thin filmtransistor having a top contact configuration.

DESCRIPTION OF THE INVENTION

Cross-sectional views of typical organic thin film transistor are shownin FIGS. 1 and 2, wherein FIG. 1 illustrates a typical bottom contactconfiguration and FIG. 2 illustrates a typical top contactconfiguration.

Each thin film transistor (TFT) in the embodiments of FIGS. 1 and 2contains a source electrode 20, a drain electrode 30, a gate electrode44, a gate dielectric 56, a substrate 28, and the semiconductor 70 ofthe invention in the form of a film connecting the source electrode 20to drain electrode 30, which semiconductor comprises a compound selectedfrom the class of N,N′-di(arylalkyl) substituted 1,4,5,8-naphthalenetetracarboxylic acid diimide compounds described herein.

When the TFT operates in an accumulation mode, the charges injected fromthe source electrode into the semiconductor are mobile and a currentflows from source to drain, mainly in a thin channel region within about100 Angstroms of the semiconductor-dielectric interface. See A.Dodabalapur, L. Torsi H. E. Katz, Science 1995, 268, 270, herebyincorporated by reference. In the configuration of FIG. 1, the chargeneed only be injected laterally from the source electrode 20 to form thechannel. In the absence of a gate field the channel ideally has fewcharge carriers; as a result there is ideally no source-drainconduction.

The off current is defined as the current flowing between the sourceelectrode 20 and the drain electrode 30 when charge has not beenintentionally injected into the channel by the application of a gatevoltage. For an accumulation-mode TFT, this occurs for a gate-sourcevoltage more negative, assuming an n-channel, than a certain voltageknown as the threshold voltage. See Sze in Semiconductor Devices—Physicsand Technology, John Wiley & Sons (1981), pages 438-443. The on currentis defined as the current flowing between the source electrode 20 andthe drain electrode 30 when charge carriers have been accumulatedintentionally in the channel by application of an appropriate voltage tothe gate electrode 44, and the channel is conducting. For an n-channelaccumulation-mode TFT, this occurs at gate-source voltage more positivethan the threshold voltage. It is desirable for this threshold voltageto be zero, or slightly positive, for n-channel operation. Switchingbetween on and off is accomplished by the application and removal of anelectric field from the gate electrode 44 across the gate dielectric 56to the semiconductor-dielectric interface, effectively charging acapacitor.

In accordance with the invention, the organic semiconductor materialsused in the present invention, when used in the form of an n-channelfilm, can exhibit high performance under inert conditions without theneed for special chemical underlayers.

The improved n-channel semiconductor film of the present invention,comprising the N,N′-di(arylalkyl) 1,4,5,8-naphthalene-basedtetracarboxylic acid diimide compounds, preferablyN,N′-di(phenylalkyl)-1,4,5,8-naphthalene-based tetracarboxylic aciddiimide compounds, described herein, is capable of exhibiting a fieldeffect electron mobility greater than 0.5 cm²/Vs, preferably greaterthan 1.0 cm²/Vs. Most advantageously, such mobilities are exhibited inair. In fact, the N,N′-di(arylalkyl) 1,4,5,8-naphthalene-basedtetracarboxylic acid diimide compounds described have exhibitedmobilities in the range of about 0.5-5.0 cm²/Vs, for example about 2.5cm²/Vs, which are some of the highest thus far reported for n-channelsemiconductor materials. Preferably films comprising the compounds ofthe present invention exhibit a field effect electron mobility that isgreater than 0.01 cm²/Vs, preferably greater than 0.1 cm²/Vs, morepreferably greater than 0.2 cm²/Vs.

In addition, the n-channel semiconductor film of the invention iscapable of providing on/off ratios of at least 10⁴, advantageously atleast 10⁵. The on/off ratio is measured as the maximum/minimum of thedrain current as the gate voltage is swept from zero to 80 volts and thedrain-source voltage is held at a constant value of 80 volts, andemploying a silicon dioxide gate dielectric.

Moreover, these properties are attainable after repeated exposure of then-type semiconductor material to air, before film deposition, as well asexposure of the transistor device and/or the channel layer to air afterdeposition.

Without wishing to be bound by theory, there are several factors thatare believed to contribute to the desirable properties of thenaphthalene-based tetracarboxylic acid diimide compounds of the presentinvention. The solid-state structure of the material has the individualmolecules packed such that the orbitals of the conjugated naphthalenecore system containing the naphthalene ring system and/or the imidecarboxyl groups, are able to interact with adjacent molecules, resultingin high mobility. The direction of this interaction has a componentparallel to the direction of desired current flow in a device using thismaterial as the active layer. The morphology of the films formed by thematerial is substantially continuous, such that current flows throughthe material without unacceptable interruption.

The lowest lying unoccupied molecular orbital of the compound is at anenergy that allows for injection of electrons at useful voltages frommetals with reasonable work functions. This conjugated structuregenerally has a desirable lowest unoccupied molecular orbital (LUMO)energy level of about 3.5 eV to about 4.6 eV with reference to thevacuum energy level. As known in the art, LUMO energy level andreduction potential approximately describe the same characteristics of amaterial. LUMO energy level values are measured with reference to thevacuum energy level, and reduction potential values are measured insolution versus a standard electrode. An advantage for deviceapplications is that the LUMO in the crystalline solid, which is theconduction band of the semiconductor, and the electron affinity of thesolid both are measured with reference to the vacuum level. The latterparameters are usually different from the former parameters, which areobtained from solution.

As indicated above, the present invention is directed to an articlecomprising, in a thin film transistor, a thin film of organicsemiconductor material that comprises an N,N′-di(arylalkyl)-substitutednaphthalene-based tetracarboxylic diimide compound having a substitutedor unsubstituted carbocyclic aromatic ring system attached to each imidenitrogen atom through a divalent hydrocarbon group, wherein any optionalsubstituents on the aryl rings comprises at least one electron donatingorganic group, i.e., if one or more substituents are present on one orboth of the two carbocyclic ring systems, such substituents comprise atleast one electron donating group. The two carbocyclic ring systems candiffer, and each carbocyclic ring system can independently havedifferent substitution or no substitution. Preferably, however, eachcarbocyclic ring system is the same, although the substitution on eachring system, if any, may differ. Preferably, if both carbocyclic ringsystems are substituted, then both carbocyclic ring systems comprise atleast one electron donating substituent group.

In one embodiment of the invention, an n-channel semiconductor filmcomprises an N,N′-di(arylalkyl)-substituted 1,4,5,8 naphthalene-basedtetracarboxylic acid diimide compound represented by general StructureI:

wherein, X is a —CH₂— or methyl substituted —CH₂— divalent group, n=1,2, or 3, and R¹, R², R³, R⁴, and R⁵ (on a first phenyl ring) and R⁶, R⁷,R⁸, R⁹, and R¹⁰ (on a second phenyl ring) are each independently H or anelectron donating organic group. Preferably, R¹, R², R³, R⁴, R⁵, R⁶, R⁷,R⁸, R⁹, and R¹⁰ substituents on the phenyl rings comprise at least oneelectron donating substituent, more preferably an alkyl, most preferablya methyl group. Preferred organic groups include, for example, CH₃,linear or branched C2-C4 alkyl, alkylene (a monovalent unsaturatedaliphatic hydrocarbon), and alkoxy. Accordingly, none of the R¹ to R¹⁰groups is an electronegative group such as a fluorine, trifluoromethylor other fluorine-containing groups, nor an aryl substituent.Preferably, X is a divalent hydrocarbon group having 1 to 4 carbonatoms, more preferably 1 to 3 carbon atoms.

Preferably, in the above structure, at least one phenyl ring issubstituted with a single substituent (most preferably an alkyl group)that is ortho or meta to the position of the —(X)_(n)— group inStructure I linking the phenyl and imide nitrogen. More preferably, bothphenyl rings are substituted with a single substituent (most preferablyan alkyl group) that is ortho or meta to the position of the —(X)_(n)—group linking the phenyl and imide nitrogen.

It is preferred that at least two of R¹, R², R³, R⁴ and R⁵ are H and atleast two of R⁶, R⁷, R⁸, R⁹, and R¹⁰ are H. More preferred structuresare those in which at least three of R¹, R², R³, R⁴ and R⁵ are H and atleast three of R⁶, R⁷, R⁸, R⁹, and R¹⁰ are H. Preferably, at least onephenyl group is substituted with an electron donating group.

According to one embodiment, preferred structures are those in whicheither all of R¹, R³, R⁴, R⁵, R⁶, R⁸, R⁹, and R¹⁰ are H, and at leastone of, preferably both of, R² and R⁷ is an electron-donating group,preferably an alkyl group such as CH₃; or all of R², R³, R⁴, R⁵, R⁷, R⁸,R⁹, and R¹⁰ are H, and at least one of, preferably both of, R¹ and R⁶ isan electron-donating group, preferably an alkyl group such as CH₃.

In the above Structure I, a first and second dicarboxylic imide moietyis attached on opposite sides of the naphthalene nucleus, at the 1,4 and5,8 positions of the perylene nucleus, based on conventional numberingof the naphthalene nucleus. The naphthalene nucleus can be optionallysubstituted with up to four independently selected Y groups, wherein mis any integer from 0 to 4. The substituent groups Y can be an organicor inorganic group at any available position on the naphthalene nucleus.Preferably m is zero. The Y substituent groups on the naphthalenenucleus can include, for example, the following groups, which may besubstituted or unsubstituted: alkyl groups, alkenyl, alkoxy groups,halogens such as fluorine or chlorine, cyano, aryl groups, arylalkylgroups, or any other groups that do not have a significantly adverseeffect the n-type semiconductor properties of the film made from suchcompounds. It is advantageous to avoid substituents that tend tointerfere with close approach of the conjugated cores of the compoundsin a stacked arrangement of the molecules that is conducive tosemiconductor properties. Such substituents include highly branchedgroups, ring structures and groups having more than 12 atoms,particularly where such groups or rings would be oriented to pose asignificant steric barrier to the close approach of the conjugatedcores. In addition, substituent groups should be avoided thatsubstantially lower the solubility and/or volatility of the compoundssuch that the desirable fabrication processes are prevented.

Unless otherwise specifically stated, use of the term “substituted” or“substituent” means any group or atom other than hydrogen. Additionally,when the term “group” is used, it means that when a substituent groupcontains a substitutable hydrogen, it is also intended to encompass notonly the substituents unsubstituted form, but also its form to theextent it can be further substituted (up to the maximum possible number)with any other mentioned substituent group or groups (mentioned for thesame position) so long as the substituent does not destroy propertiesnecessary for semiconductor utility. If desired, the substituents maythemselves be further substituted one or more times with acceptablesubstituent groups. For example, an alkyl group can be substituted withan alkoxy group, in the case of an R group (R¹ to R¹⁰), or one or morefluorine atoms in the case of a Y group. When a molecule may have two ormore substituents, the substituents may be joined together to form analiphatic or unsaturated ring unless otherwise provided.

With respect to the R groups or Y groups, examples of any of theabove-mentioned alkyl groups, except as otherwise indicated, are methyl,ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl,octyl, 2-ethylhexyl, and congeners. Alkyl groups, preferably having 1 to6 carbon atoms, more preferably 1 to 4, are intended to include branchedor linear groups. Alkenyl groups can be vinyl, 1-propenyl, 1-butenyl,2-butenyl, and congeners.

With respect to Y groups, aryl groups can be phenyl, naphthyl, styryl,and congeners. Arylalkyl groups can be benzyl, phenethyl, and congeners.Useful substituents on any of the foregoing include halogen, and alkoxy,and the like. Y substituents on the naphthalene nucleus or core can beeither electron-withdrawing groups and/or electron-donating groups.

When referring to electron donating groups, this can be indicated orestimated by the Hammett substituent constant (σ_(p), σ_(m)), asdescribed by L. P. Hammett in Physical Organic Chemistry (McGraw-HillBook Co., NY, 1940), or by the Taft polar substituent constants (σ_(i))as defined by R. W. Taft in Steric Effects in Organic Chemistry (Wileyand Sons, NY, 1956), and in other standard organic textbooks. Thisparameter which characterizes the ability of ring-substituents (in thepara position) to affect the electronic nature of a reaction site, wereoriginally quantified by their effect on the pKa of benzoic acid.Subsequent work has extended and refined the original concept and data,but for the purposes of prediction and correlation, standard sets ofσ_(p) are widely available in the chemical literature, as for example inC. Hansch et al., J. Med. Chem., 17, 1207 (1973). Preferably, anelectron donating group has a σ_(p) or σ_(m) of less than zero, morepreferably less than −0.05, most preferably less than −0.1. The σ_(p)value can be used to indicate the electron donating nature of the groupin a structure according to the present invention, as in Structure Iabove even when the group is not a para substituent in Structure I.

Specific illustrative examples of useful N,N′-substituted 1,4,5,8naphthalene-based tetracarboxylic acid diimide derivatives are shown bythe formulae below: I-1

I-2

I-3

I-4

I-5

I-6

I-7

I-8

I-9

I-10

I-11

I-12

I-13

I-14

I-15

Symmetrical N,N′-dialkyl naphthalene tetracarboxylic acid diimides usedin this invention are conveniently prepared by cyclizing naphthalenetetracarboxylic acid dianhydride with excess of suitable amines such asphenylethyl amine. Typical procedures are described in Eur. Pat. Appl.EP 251071 and U.S. Pat. No. 4,156,757 and in U.S. Pat. Nos. 4,578,334and 4,719,163. Typical procedures for preparing unsymmetricalnaphthalene tetracarboxylic acid diimides are described in U.S. Pat. No.4,714,666. The crude materials were then purified by train sublimationat 10⁻⁵ to 10⁻⁶ torr.

Another aspect of the invention relates to the process for theproduction of semiconductor components and electronic devicesincorporating such components. In one embodiment, a substrate isprovided and a layer of the semiconductor material as described abovecan be applied to the substrate, electrical contacts being made with thelayer. The exact process sequence is determined by the structure of thedesired semiconductor component. Thus, in the production of an organicfield effect transistor, for example, a gate electrode can be firstdeposited on a flexible substrate, for example an organic polymer film,the gate electrode can then be insulated with a dielectric and thensource and drain electrodes and a layer of the n-channel semiconductormaterial can be applied on top. The structure of such a transistor andhence the sequence of its production can be varied in the customarymanner known to a person skilled in the art. Thus, alternatively, a gateelectrode can be deposited first, followed by a gate dielectric, thenthe organic semiconductor can be applied, and finally the contacts forthe source electrode and drain electrode deposited on the semiconductorlayer. A third structure could have the source and drain electrodesdeposited first, then the organic semiconductor, with dielectric andgate electrode deposited on top.

The skilled artisan will recognize other structures can be constructedand/or intermediate surface modifying layers can be interposed betweenthe above-described components of the thin film transistor. In mostembodiments, a field effect transistor comprises an insulating layer, agate electrode, a semiconductor layer comprising an organic material asdescribed herein, a source electrode, and a drain electrode, wherein theinsulating layer, the gate electrode, the semiconductor layer, thesource electrode, and the drain electrode are in any sequence as long asthe gate electrode and the semiconductor layer both contact theinsulating layer, and the source electrode and the drain electrode bothcontact the semiconductor layer.

A support can be used for supporting the OTFT during manufacturing,testing, and/or use. The skilled artisan will appreciate that a supportselected for commercial embodiments may be different from one selectedfor testing or screening various embodiments. In some embodiments, thesupport does not provide any necessary electrical function for the TFT.This type of support is termed a “non-participating support” in thisdocument. Useful materials can include organic or inorganic materials.For example, the support may comprise inorganic glasses, ceramic foils,polymeric materials, filled polymeric materials, coated metallic foils,acrylics, epoxies, polyamides, polycarbonates, polyimides, polyketones,poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene)(sometimes referred to as poly(ether ether ketone) or PEEK),polynorbornenes, polyphenyleneoxides, poly(ethylenenaphthalenedicarboxylate) (PEN), poly(ethylene terephthalate) (PET),poly(phenylene sulfide) (PPS), and fiber-reinforced plastics (FRP).

A flexible support is used in some embodiments of the present invention.This allows for roll processing, which may be continuous, providingeconomy of scale and economy of manufacturing over flat and/or rigidsupports. The flexible support chosen preferably is capable of wrappingaround the circumference of a cylinder of less than about 50 cmdiameter, more preferably 25 cm diameter, most preferably 10 cmdiameter, without distorting or breaking, using low force as by unaidedhands. The preferred flexible support may be rolled upon itself.

In some embodiments of the invention, the support is optional. Forexample, in a top construction as in FIG. 2, when the gate electrodeand/or gate dielectric provides sufficient support for the intended useof the resultant TFT, the support is not required. In addition, thesupport may be combined with a temporary support. In such an embodiment,a support may be detachably adhered or mechanically affixed to thesupport, such as when the support is desired for a temporary purpose,e.g., manufacturing, transport, testing, and/or storage. For example, aflexible polymeric support may be adhered to a rigid glass support,which support could be removed.

The gate electrode can be any useful conductive material. A variety ofgate materials known in the art, are also suitable, including metals,degenerately doped semiconductors, conducting polymers, and printablematerials such as carbon ink or silver-epoxy. For example, the gateelectrode may comprise doped silicon, or a metal, such as aluminum,chromium, gold, silver, nickel, palladium, platinum, tantalum, andtitanium. Conductive polymers also can be used, for example polyaniline,poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS). Inaddition, alloys, combinations, and multilayers of these materials maybe useful.

In some embodiments of the invention, the same material can provide thegate electrode function and also provide the support function of thesupport. For example, doped silicon can function as the gate electrodeand support the OTFT.

The gate dielectric is provided on the gate electrode. This gatedielectric electrically insulates the gate electrode from the balance ofthe OTFT device. Thus, the gate dielectric comprises an electricallyinsulating material. The gate dielectric should have a suitabledielectric constant that can vary widely depending on the particulardevice and circumstance of use. For example, a dielectric constant fromabout 2 to 100 or even higher is known for a gate dielectric. Usefulmaterials for the gate dielectric may comprise, for example, aninorganic electrically insulating material. The gate dielectric maycomprise a polymeric material, such as polyvinylidenedifluoride (PVDF),cyanocelluloses, polyimides, etc. The gate electric may comprise aplurality of layers of different materials having different dielectricconstants.

Specific examples of materials useful for the gate dielectric includestrontiates, tantalates, titanates, zirconates, aluminum oxides, siliconoxides, tantalum oxides, titanium oxides, silicon nitrides, bariumtitanate, barium strontium titanate, barium zirconate titanate, zincselenide, and zinc sulfide. In addition, alloys, combinations, andmultilayers of these examples can be used for the gate dielectric. Ofthese materials, aluminum oxides, silicon oxides, and zinc selenide arepreferred. In addition, polymeric materials such as polyimides, andinsulators that exhibit a high dielectric constant. Such insulators arediscussed in U.S. Pat. No. 5,981,970 hereby incorporated by reference.

The gate dielectric can be provided in the OTFT as a separate layer, orformed on the gate such as by oxidizing the gate material to form thegate dielectric. The dielectric layer may comprise two or more layershaving different dielectric constants.

The source electrode and drain electrode are separated from the gateelectrode by the gate dielectric, while the organic semiconductor layercan be over or under the source electrode and drain electrode. Thesource and drain electrodes can be any useful conductive material.Useful materials include most of those materials described above for thegate electrode, for example, aluminum, barium, calcium, chromium, gold,silver, nickel, palladium, platinum, titanium, polyaniline, PEDOT:PSS,other conducting polymers, alloys thereof, combinations thereof, andmultilayers thereof.

The thin film electrodes (e.g., gate electrode, source electrode, anddrain electrode) can be provided by any useful means such as physicalvapor deposition (e.g., thermal evaporation, sputtering) or ink jetprinting. The patterning of these electrodes can be accomplished byknown methods such as shadow masking, additive photolithography,subtractive photolithography, printing, microcontact printing, andpattern coating.

The organic semiconductor layer can be provided over or under the sourceand drain electrodes, as described above in reference to the thin filmtransistor article. The present invention also provides an integratedcircuit comprising a plurality of OTFTs made by the process describedherein. The n-channel semiconductor material made using theabove-described N,N′-substituted 1,4,5,8-naphthalene-basedtetracarboxylic acid diimide compounds are capable of being formed onany suitable substrate which can comprise the support and anyintermediate layers such as a dielectric or insulator material,including those known in the art.

The entire process of making the thin film transistor or integratedcircuit of the present invention can be carried out below a maximumsupport temperature of about 450° C., preferably below about 250° C.,more preferably below about 150° C., and even more preferably belowabout 100° C., or even at temperatures around room temperature (about25° C. to 70° C.). The temperature selection generally depends on thesupport and processing parameters known in the art, once one is armedwith the knowledge of the present invention contained herein. Thesetemperatures are well below traditional integrated circuit andsemiconductor processing temperatures, which enables the use of any of avariety of relatively inexpensive supports, such as flexible polymericsupports. Thus, the invention enables production of relativelyinexpensive integrated circuits containing organic thin film transistorswith significantly improved performance.

Compounds used in the invention can be readily processed and arethermally stable to such as extent that they can be vaporized. Thecompounds possess significant volatility, so that vapor phasedeposition, where desired, is readily achieved. Such compounds can bedeposited onto substrates by vacuum sublimation.

Deposition by a rapid sublimation method is also possible. One suchmethod is to apply a vacuum of 35 mtorr to a chamber containing asubstrate and a source vessel that holds the compound in powdered form,and heat the vessel over several minutes until the compound sublimesonto the substrate. Generally, the most useful compounds formwell-ordered films, with amorphous films being less useful.

Devices in which the n-channel semiconductor films of the invention areuseful include especially thin film transistors (TFTs), especiallyorganic field effect thin-film transistors. Also, such films can be usedin various types of devices having organic p-n junctions, such asdescribed on pages 13 to 15 of US 2004,0021204 A1 to Liu, which patentis hereby incorporated by reference.

Electronic devices in which TFTs and other devices are useful include,for example, more complex circuits, e.g., shift registers, integratedcircuits, logic circuits, smart cards, memory devices, radio-frequencyidentification tags, backplanes for active matrix displays,active-matrix displays (e.g. liquid crystal or OLED), solar cells, ringoscillators, and complementary circuits, such as inverter circuits, forexample, in combination with other transistors made using availablep-type organic semiconductor materials such as pentacene. In an activematrix display, a transistor according to the present invention can beused as part of voltage hold circuitry of a pixel of the display. Indevices containing the TFTs of the present invention, such TFTs areoperatively connected by means known in the art.

The present invention further provides a method of making any of theelectronic devices described above. Thus, the present invention isembodied in an article that comprises one or more of the TFTs described.

Advantages of the invention will be demonstrated by the followingexamples, which are intended to be exemplary.

EXAMPLES

A. Material Synthesis

The N,N′-di(arylalkyl)-1,4,5,8-naphthalene tetracarboxylic acid diimidesused in this invention are conveniently prepared by cyclizingnaphthalene tetracarboxylic acid dianhydride with excess2-para-tolyl-ethylamine following a general method described inRademacher, A. et al. Chem. Ber. 1982 115, 2927. For example,N,N′-di(4-methylphenyl)ethyl-1,4,5,8-naphthalene tetracarboxylic aciddiimide (Compound I-4) used in this invention is conveniently preparedby cyclizing naphthalene tetracarboxylic acid dianhydride with excess2-para-tolyl-ethylamine. Accordingly, a mixture of naphthalenetetracarboxylic acid dianhydride, which is available from AldrichChemical Company, 3-4 equivalents excess of an amine, for example2-para-tolyl-ethylamine, also available from Aldrich, zinc acetate incatalytic amounts, and 10-15 ml of quinoline per gram of dianhydridemolecule was heated over 4-5 hours at a temperature of ca. 220° C. Themixture is allowed to cool to room temperature, and the precipitatedsolids are collected, filtered and washed with acetone, followed by 200ml each of boiling 0.1 M aqueous Na₂CO₃, boiling water, and warmtoluene, that is kept below the temperature at which the product wouldbe substantially dissolved. The solid is then purified by trainsublimation at 10⁻⁵ to 10⁻⁶ torr. (As described above, other compoundsare conveniently prepared by cyclizing naphthalene tetracarboxylic aciddianhydride with excess of the suitable amine.) The crude materials werethen purified by train sublimation at 10⁻⁵ to 10⁻⁶ torr.

B. Device Preparation

In order to test the electrical characteristics of the various materialsof this invention, field-effect transistors were typically made usingthe top-contact geometry. The substrate used is a heavily doped siliconwafer, which also serves as the gate of the transistor. The gatedielectric is a thermally grown SiO₂ layer with a thickness of 185 nm.It has been previously shown for both p-type and n-type transistors thatelectrical properties can be improved by treating the surface of thegate dielectric. For most of the experiments described here, the oxidesurface was treated with a thin (<10 nm), spin-coated polymer layer, ora self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS).Typically, an untreated oxide sample was included in the experiments forcomparison.

The active layer of naphthalene tetracarboxylic acid diimide wasdeposited via vacuum deposition in a thermal evaporator. The depositionrate was 0.1 Angstroms per second while the substrate temperature washeld at 90° C. for most experiments. The thickness of the active layerwas a variable in some experiments, but was typically 25 nm. Silvercontacts of thickness 50 nm were deposited through a shadow mask. Thechannel width was held at 420 microns, while the channel lengths werevaried between 50 and 175 microns. Some experiments were performed tolook at the effect of other contact materials. A few devices were madewith a bottom-contact geometry, in which the contacts were depositedprior to the active material.

C. Device Measurement and Analysis

Electrical characterization of the fabricated devices was performed witha Hewlett Packard HP 4145b® parameter analyzer. The probe measurementstation was held in a positive argon environment for all measurementswith the exception of those purposely testing the stability of thedevices in air. The measurements were performed under sulfur lightingunless sensitivity to white light was being investigated. The deviceswere exposed to air prior to testing.

For each experiment performed, between 4 and 12 individual devices weretested on each sample prepared, and the results were averaged. For eachdevice, the drain current (Id) was measured as a function ofsource-drain voltage (Vd) for various values of gate voltage (Vg). Formost devices, Vd was swept from 0 V to 80 V for each of the gatevoltages measured, typically 0 V, 20 V, 40 V, 60 V, and 80 V. In thesemeasurements, the gate current (Ig) was also recorded in order to detectany leakage current through the device. Furthermore, for each device thedrain current was measured as a function of gate voltage for variousvalues of source-drain voltage. For most devices, Vg was swept from 0 Vto 80 V for each of the drain voltages measured, typically 40 V, 60 V,and 80 V.

Parameters extracted from the data include field-effect mobility (μ),threshold voltage (Vth), subthreshold slope (S), and the ratio ofIon/Ioff for the measured drain current. The field-effect mobility wasextracted in the saturation region, where Vd>Vg−Vth. In this region, thedrain current is given by the equation (see Sze in SemiconductorDevices—Physics and Technology, John Wiley & Sons (1981)):$I_{d} = {\frac{W}{2L}\mu\quad{C_{ox}\left( {V_{g} - V_{th}} \right)}^{2}}$Where, W and L are the channel width and length, respectively, andC_(ox) is the capacitance of the oxide layer, which is a function ofoxide thickness and dielectric constant of the material. Given thisequation, the saturation field-effect mobility was extracted from astraight-line fit to the linear portion of the √I_(d) versus Vg curve.The threshold voltage, V_(th), is the x-intercept of this straight-linefit. Mobilities can also be extracted from the linear region, whereVd≦Vg−Vth. Here the drain current is given by the equation (see Sze inSemiconductor Devices—Physics and Technology, John Wiley & Sons (1981)):$I_{d} = {\frac{W}{L}\mu\quad{C_{ox}\left\lbrack {{V_{d}\left( {V_{g} - V_{th}} \right)} - \frac{V_{d}^{2}}{2}} \right\rbrack}}$

For these experiments, mobilities in the linear regime were notextracted, since this parameter is very much affected by any injectionproblems at the contacts. In general, non-linearities in the curves ofI_(d) versus V_(d) at low V_(d) indicate that the performance of thedevice is limited by injection of charge by the contacts. In order toobtain results that are largely independent of contact imperfections ofa given device, the saturation mobility rather than the linear mobilitywas extracted as the characteristic parameter of device performance.

The log of the drain current as a function of gate voltage was plotted.Parameters extracted from the log I_(d) plot include the I_(on)/I_(off)ratio and the sub-threshold slope (S). The I_(on)/I_(off) ratio issimply the ratio of the maximum to minimum drain current, and S is theinverse of the slope of the I_(d) curve in the region over which thedrain current is increasing (i.e. the device is turning on).

D. Results

The following examples demonstrate that compared toN,N′-diphenyl-1,4,5,8-naphthalene tetracarboxylic acid diimide,inventive devices comprising arylalkyl-containingN,N′-substituted-1,4,5,8-naphthalene-based tetracarboxylic acid diimidesprovide improved n-channel semiconductor films having high mobility andon/off ratio. The mobility calculated in the saturation region wasbetween 0.07 and 2.5 cm²/Vs, with an on/off ratio of 10⁴ to 10⁵. Inaddition to the improved performance, the devices also show improvedstability in air relative to typical n-channel TFTs, and excellentreproducibility.

Comparison Example 1

This example demonstrates the n-type TFT device made from anN,N′-diphenyl-1,4,5,8-naphthalene tetracarboxylic acid diimide C-1:

A heavily doped silicon wafer with a thermally-grown SiO₂ layer with athickness of 185 nm was used as the substrate. The wafer was cleaned for10 minutes in a piranah solution, followed by a 6-minute exposure in aUV/ozone chamber. The cleaned surface was then treated with aself-assembled monolayer of octadecyltrichlorosilane (OTS), made from aheptane solution under a humidity-controlled environment. Water contactangles and layer thicknesses were measured to ensure the quality of thetreated surface. Surfaces with a good quality OTS layer have watercontact angles >90°, and thicknesses determined from ellipsometry in therange of 27 Å to 35 Å.

The purified N,N′-diphenyl-1,4,5,8-naphthalene tetracarboxylic aciddiimide C-1 was deposited by vacuum sublimation at a pressure of 2×10⁻⁷Torr and a rate of 0.1 Angstroms per second to a thickness of 25 nm asmeasured by a quartz crystal. During deposition the substrate was heldat a constant temperature of 90° C. The sample was exposed to air for ashort time prior to subsequent deposition of Ag source and drainelectrodes through a shadow mask to a thickness of 50 nm. The devicesmade had a 420 micron channel width, with channel lengths varying from50 to 175 microns. Multiple OTFTs were prepared and representativesamples of 4 to 12 OTFTs were tested for each deposition run. Theaveraged results appear in Table 1 below.

The devices were exposed to air prior to measurement in an argonatmosphere using a Hewlett-Packard 4145B® semiconductor parameteranalyzer. For each transistor, the field effect mobility, μ, wascalculated from the slope of the (I_(D))^(1/2) versus V_(G) plot. Theaverage mobility was found to be 0.064 cm²/Vs in the saturation region.The average on-off ratio was 2.3×10⁴′ and the average threshold voltagewas 57.3V. Saturation mobilities of up to 0.12 cm²/Vs were measured fordevices prepared in this way.

Example 2

This example demonstrates the improved performance of an n-type TFTdevice using N,N′-di(phenylethyl)-1,4,5,8-naphthalene tetracarboxylicacid diimide, Compound I-1 in accordance with the present invention.

An n-type TFT device comprising Compound I-1 as the active material wasmade as in Example 1. Accordingly, compound I-1 was deposited by vacuumsublimation at a pressure of 2×10⁻⁷ Torr and a rate of 0.1 Angstroms persecond to a thickness of 25 nm as measured by a quartz crystal. Duringdeposition the substrate was held at a constant temperature of 90° C.The sample was exposed to air for a short time prior to subsequentdeposition of Ag source and drain electrodes through a shadow mask to athickness of 50 nm. The devices made had an approximately 420 micronchannel width, with channel lengths varying from 50 to 175 microns.Multiple organic thin film transistors (OTFTs) were prepared andrepresentative sample of 4 to 12 OTFTs were tested for each depositionrun. The averaged results appear in Table 1 below.

The devices were exposed to air prior to measurement in an argonatmosphere using a Hewlett-Packard 4145B® semiconductor parameteranalyzer. The average field effect mobility, μ, was calculated from theslope of the (I_(D))^(1/2) versus V_(G) plot to be 0.13 cm²/Vs in thesaturation region. The average on/off ratio was 4.8×10⁴ and the averagethreshold voltage V_(T)=61.3 V. Saturation mobilities of up to 0.46cm²/Vs were measured from similar devices prepared in this way. TABLE 1Active OTFT μ σ V_(th) σ Material (cm²/Vs) (μ) (V) (V_(th))I_(on)/I_(off) Comparison C-1 0.064 0.037 57.3 3.6 2.3 × 10⁴ Example 1Inventive I-1 0.132 0.170 61.25 3.91 4.78 × 10⁴  Example 2

This example clearly demonstrates the advantage of using Compound I-1 asn-type material. The mobility is improved over Comparison Example 1,clearly demonstrating the effect of —CH₂—CH₂— groups between diimidenitrogen and phenyl ring on device performance.

Example 3

This example demonstrates the improved performance n-type TFT devicemade from a fluorine-containingN,N′-di(4-methylphenyl)ethyl-1,4,5,8-naphthalene tetracarboxylic aciddiimide, Compound I-4. An n-type TFT device using compound I-4 as theactive material of the OTFT was made as in Example 1. Multiple OTFTswere prepared and tested for each deposition run. The averaged resultsappear in Table 2 below. TABLE 2 Active OTFT μ σ V_(th) σ Material(cm²/Vs) (μ) (V) (V_(th)) I_(on)/I_(off) Comparative C-1 0.064 0.03757.3 3.6 2.3 × 10⁴ Example 1 Inventive I-4 0.143 0.076 55.8 2.5 3.0 ×10⁴ Example 3

This example clearly demonstrates the advantage of Compound I-4 asn-type material. The mobility is improved over Comparative Example 1,clearly demonstrating the beneficial effect of the (4-methylphenyl)ethylgroups on device performance.

Example 4

This example demonstrates the improved performance n-type TFT devicemade from N,N′-di(3-methylbenzyl)-1,4,5,8-naphthalene tetracarboxylicacid diimide, Compound I-10. An n-type TFT device using Compound I-10 asthe active material of the OTFT was made as in Example 1. Multiple OTFTswere prepared and tested for each deposition run. The averaged resultsappear in Table 3 below. TABLE 3 Active OTFT μ σ V_(th) σ Material(cm²/Vs) (μ) (V) (V_(th)) I_(on)/I_(off) Comparison C-1 0.064 0.037 57.33.6 2.3 × 10⁴ Example 1 Inventive I-10 0.07 0.035 53.6 2.0 5.4 × 10⁴Example 4

This example clearly demonstrates the advantage of Compound I-10 asn-type material. From the slope of the (I_(D))^(1/2) versus V_(G) plotsaturation region mobilities of up to 0.12 cm²/Vs were measured fromsimilar devices prepared in this way.

Example 5

This example demonstrates the improved performance n-type TFT devicemade from N,N′-di(2-phenyl-propyl)-1,4,5,8-naphthalene tetracarboxylicacid diimide, Compound I-15. An n-type TFT device using Compound I-15 asthe active material of the OTFT was made as in Example 1. Multiple OTFTswere prepared and tested for each deposition run. The averaged resultsappear in Table 4 below. TABLE 4 Active OTFT μ σ V_(th) σ Material(cm²/Vs) (μ) (V) (V_(th)) I_(on)/I_(off) Comparison C-1 0.064 0.037 57.33.6 2.3 × 10⁴ Example 1 Inventive I-15 0.098 0.035 52.5 3.1 4.9 × 10⁴Example 4

This example clearly demonstrates the advantage of Compound I-15 asn-type material. From the slope of the (I_(D))^(1/2) versus V_(G) plotsaturation region mobilities of up to 0.14 cm²/Vs were measured fromsimilar devices prepared in this way.

Example 6

This example demonstrates the improved performance n-type TFT devicemade from N,N′-di(3-methylphenyl)ethyl-1,4,5,8-naphthalenetetracarboxylic acid diimide, Compound I-2. An n-type TFT device usingCompound I-2 as the active material of the OTFT was made as inExample 1. Multiple OTFTs were prepared and tested for each depositionrun. The averaged results appear in Table 5 below. TABLE 5 Active OTFT μσ V_(th) σ Material (cm²/Vs) (μ) (V) (V_(th)) I_(on)/I_(off) ComparisonC-1 0.064 0.037 57.3 3.6 2.3 × 10⁴ Example 1 Inventive I-2 2.47 0.73644.0 8.4 7.0 × 10⁵ Example 4

This example clearly demonstrates the advantage of Compound I-2 asn-type material. From the slope of the (I_(D))^(1/2) versus V_(G) plotsaturation region mobilities of up to 3.3 cm²/Vs were measured fromsimilar devices prepared in this way.

PARTS LIST

-   20 source electrode-   28 substrate-   30 drain electrode-   44 gate electrode-   56 gate dielectric-   70 semiconductor

1. An article comprising, in a thin film transistor, a thin film oforganic semiconductor material that comprises anN,N′-di(arylalkyl)-substituted naphthalene tetracarboxylic diimidecompound having a substituted or unsubstituted carbocyclic aromatic ringsystem attached to each imide nitrogen atom through a divalenthydrocarbon group, wherein substituents, if any, on each carbocyclicaromatic ring system are independently selected electron donatingorganic substituents.
 2. The article of claim 1 wherein the thin filmtransistor is a field effect transistor comprising a dielectric layer, agate electrode, a source electrode and a drain electrode, and whereinthe dielectric layer, the gate electrode, the thin film of organicsemiconductor material, the source electrode, and the drain electrodeare in any sequence as long as the gate electrode and the film oforganic semiconductor material both contact the dielectric layer, andthe source electrode and the drain electrode both contact the thin filmof the organic semiconductor material.
 3. The article of claim 1 whereinthe thin film of organic semiconducting material is capable ofexhibiting electron mobility greater than 0.01 cm²/Vs.
 4. The article ofclaim 1, wherein the thin film of organic semiconductor materialcomprises a N,N′-di(arylalkyl)-substituted-1,4,5,8-naphthalenetetracarboxylic acid diimide compound represented by the followingstructure:

wherein, X is a —CH₂— or alkyl substituted —CH₂— divalent group, n=1, 2,or 3, and R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, and R¹⁰, on a first andsecond ring system in the structure, are each independently H or anelectron donating organic group, wherein optionally two adjacent groupson said first or second ring system can form a fused aromatic ring. 5.The article of claim 4 wherein either one or both of the first andsecond ring systems, in said structure, are substituted with at leastone electron donating group.
 6. The article of claim 5 wherein the atleast one electron donating group is an alkyl group.
 7. The article ofclaim 4, wherein in said structure R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹,and R¹⁰ are each independently selected from H, CH₃, linear or branchedC₂-C₄ alkyl, alkenyl, alkoxy, or other electron donating organic grouphaving 1 to 4 carbon atoms.
 8. The article of claim 4, wherein in saidstructure at least two of R¹, R², R³, R⁴ and R⁵ are H and at least twoof R⁶, R⁷, R⁸, R⁹, and R¹⁰ are H.
 9. The article of claim 8, wherein insaid structure at least three of R¹, R², R³, R⁴ and R⁵ are H and atleast three of R⁶, R⁷, R⁸, R⁹, and R¹⁰ are H.
 10. The article of claim1, wherein in said structure either all of R¹, R³, R⁴, R⁵, R⁶, R⁸, R⁹,and R¹⁰ are H, and at least one of R² and R⁷ is an alkyl group; or allof R², R³, R⁴, R⁵, R⁷, R⁸, R⁹, and R¹⁰ are H, and at least one of R¹ andR⁶ are CH₃.
 11. The article of claim 10, wherein in said structure thefirst and second ring system is a substituted or unsubstituted unfusedphenyl ring.
 12. The article of claim 11, wherein in said structure atleast one phenyl ring is substituted with a single substituent that isortho or meta to the position of the —(X)_(n)— group linking the phenyland imide nitrogen.
 13. The article of claim 11, wherein in saidstructure both phenyl rings are substituted with a single substituentthat is ortho or meta to the position of the —(X)_(n)— group linking thephenyl and imide nitrogen.
 14. The article of claim 4 wherein Y isindependently selected from alkyl, alkenyl, and alkoxy groups.
 15. Thearticle of claim 1, wherein the thin film transistor has an on/off ratioof a source/drain current of at least 10⁴.
 16. The article of claim 2,wherein the gate electrode is adapted for controlling, by means of avoltage applied to the gate electrode, a current between the source anddrain electrodes through the thin film of organic semiconductormaterial.
 17. The article of claim 16 wherein the gate dielectriccomprises an inorganic or organic electrically insulating material. 18.The article of claim 1 wherein the thin film transistor furthercomprises a non-participating support that is optionally flexible. 19.The article of claim 2 wherein the source, drain, and gate electrodeseach independently comprise a material selected from doped silicon,metal, and a conducting polymer.
 20. An electronic device selected fromthe group consisting of integrated circuits, active-matrix display, andsolar cells comprising a multiplicity of thin film transistors accordingto claim
 1. 21. The electronic device of claim 20 wherein themultiplicity of the thin film transistors is on a non-participatingsupport that is optionally flexible.
 22. A process for fabricating athin film semiconductor device, comprising, not necessarily in thefollowing order, the steps of: (a) depositing, onto a substrate, a thinfilm of n-channel organic semiconductor material that comprises anN,N′-di(arylalkyl)-substituted-naphthalene tetracarboxylic diimidecompound having a substituted or unsubstituted carbocyclic aromatic ringsystem attached to each imide nitrogen atom through a divalenthydrocarbon group, wherein substituents, if any, on each carbocyclicaromatic ring system are electron donating organic groups, such that theorganic semiconductor material exhibits a field effect electron mobilitythat is greater than 0.01 cm²/Vs; (b) forming a spaced apart sourceelectrode and drain electrode, wherein the source electrode and thedrain electrode are separated by, and electrically connected with, then-channel semiconductor film; and. (c) forming a gate electrode spacedapart from the organic semiconductor material.
 23. The process of claim22, wherein said compound is deposited on the substrate by sublimationand wherein the substrate has a temperature of no more than 100° C.during deposition.
 24. The process of claim 22 wherein there is no priortreatment of interfaces between the electrodes and the thin film ofn-channel organic semiconductor material.
 25. The process of claim 22wherein the compound isN,N′-bis[2-methyl-phenylethyl]-naphthalene-1,4,5,8 tetracarboxylic aciddiimide, N,N′-bis[3-methyl-phenylethyl]-naphthalene-1,4,5,8tetracarboxylic acid diimide, orN,N′-bis[2-methyl-phenylmethyl]-naphthalene-1,4,5,8-tetracarboxylic aciddiimide orN,N′-bis[3-methyl-phenylmethyl]-naphthalene-1,4,5,8-tetracarboxylic aciddiimide or N-(2-methyl-phenylethyl),N′-(phenylethyl)-naphthalene-1,4,5,8-tetracarboxylic acid diimide. 26.The process of claim 22 comprising, not necessarily in order, thefollowing steps: (a) providing a substrate; (b) providing a gateelectrode material over the substrate (c) providing a gate dielectricover the gate electrode material; (d) depositing the thin film ofn-channel organic semiconductor material over the gate dielectric: (e)providing a source electrode and a drain electrode contiguous to thethin film of n-channel organic semiconductor material.
 27. The processof claim 26 wherein the steps are performed in the order listed.
 28. Theprocess of claim 26 wherein the substrate is flexible.
 29. The processof claim 26 carried out in its entirety below a peak temperature of 100°C.
 30. An integrated circuit comprising a plurality of thin filmtransistors made by the process of claim 22.